Bioactive peptides are specific fragments of proteins that are thought to have certain physiological benefits for human health. Bioactive peptides are latent in intact proteins but can be released through in vitro or in vivo enzymatic hydrolysis from the parent food proteins. For example, milk has been identified to contain numerous bioactive proteins and peptides. Such bioactive proteins include lactoferrin, caseins, colostrums, and praventin. See Maruyama, S.; Mitachi, H.; Tanaka, H.; Tomizuka, N.; Suzuki, H. Studies on the active site and antihypertensive activity of angiotensin I-converting enzyme inhibitors derived from casein. Agricultural Biological Chemistry 1998, 51, 1581-1586; FitzGerald, R. J.; Murray, B. A.; Walsh, D J. Hypotensive peptides from milk proteins. Journal of Nutrition 2004, 134, 980S-988S; which is hereby incorporated by reference in its entirety. It is speculated that these peptides have an antihypertensive effect and play a role in reducing or inhibiting the Angiotensin Converting Enzyme (ACE).
Angiotensin converting enzyme (ACE) is the key enzyme responsible for the regulation of blood pressure through rennin-angiotensin system. ACE catalyses the formation of angiotensin II, a potent vasoconstrictor, from angiotensin I and inactivates bradykinin, a vasodilator. Elevated activity of ACE could lead to a higher level of angiotensin II and therefore cause high blood pressure or hypertension. Inhibition of ACE is a therapeutic strategy for antihypertension drug development. Currently, ACE inhibitory drugs are the first line therapy of hypertension. Although synthetic ACE inhibitors, such as captopril and enalapril, are widely used as anti-hypertensive drugs, they inevitably cause adverse side effects including chronic coughing and angioedima.
In addition to milk proteins, egg proteins are thought to be a rich source of bioactive proteins and bioactive peptides. Egg proteins are one of the major sources of dietary nitrogen. In egg, proteins are distributed throughout both the egg white and yolk. It is theorized that proteins within egg have numerous biological activities including antimicrobial activity, anticancer activity, and protease inhibition, and it is further thought that egg proteins are an excellent source of bioactive peptides including antihypertensive peptides.
For example, ovotransferrin is one of the major proteins in egg white, accounting for approximately 13% of the overall protein in egg white. However, due to ovotransferrin's amino acid sequence (i.e. having high sulfur content and numerous disulfide bridges), native ovotransferrin is resistant to heat and enzymatic hydrolysis. Therefore, it is generally difficult to convert naturally occurring proteins into bioactive peptides that possess health benefits.